Monday, August 02, 2010

A "Canseco Effect" study

Did Jose Canseco influence his teammates to use steroids? Canseco loudly claimed that he did, and the claim seems plausible. But do the numbers back him up?

A couple of years ago, in an academic paper, two Israeli economists said they do. Eric D. Gould and Todd R. Kaplan ran regressions on individual player-seasons, and claimed that after playing with Canseco, players in general hit for more power. Furthermore, the result didn't hold for other players. For instance, after playing with Ken Griffey Jr., Junior's teammates' home runs actually fell, instead of rising.

The paper was recently reviewed -- uncritically -- in Slate. In response, J.C. Bradbury reposted his original critique of the study. JC's response is right on the money -- he shows that the results aren't very robust, and wonders why the authors used raw home run totals instead of rates (which is especially egregious considering that their minimum was only 50 AB). I suggest reading JC's post before continuing here.

The study's most important finding is that, after Canseco left a team, his average ex-teammate improved by almost three home runs a year. That's a large improvement (and statistically significant at 4.5 SDs).

But, for the most part, the reason they hit more home runs is just that they got more playing time! In Table 7, the study shows that those players who hit 3 more HR also had 53 more AB. You might have expected those guys to hit, what, maybe 2 HR in the extra 53 AB, instead of 3? So the difference Canseco makes is ... one home run. Two HR due to playing time, but only one that could possibly be attributed to a change in performance level.

What caused that extra home run? It's a long stretch to insist it's due to steroid use, and it's almost as long a stretch to even say that it's something unique about Canseco. Because, look at the numbers for some of the other players in the same chart.

Ken Griffey looks like the anti-Canseco. After playing with Griffey, his ex-teammates wound up with 46 fewer AB than before, and their homers dropped by 3.4. But with 46 fewer AB, their expected drop should only have been about 2 HR, not 3.4. So it looks like Griffey reduced his former teammates' output by about 1.4 home runs.

If you want to believe that the extra 1 HR is due Canseco pushing his teammates to try steroids, does that mean that Griffey's negative 1.4 HR must have been because he pushed his teammates to *quit* steroids, and he did it 30% better than Canseco did?

Or, look at Ryne Sandberg's teammates. Those guys also lost playing time after their Sandberg teammateship, by 24 AB. But even with fewer at-bats, they *gained* 1.6 HRs! So Sandberg's effect on his teammates was more than two-and-a-half times as large as Canseco's. So, did Sandberg push PEDs 250% as hard as Canseco did?

So far, I think it's clear that these numbers don't necessarily have anything to do with steroids. Especially because there's a better explanation, at least for the changes in AB.

Ryne Sandberg played almost his entire career for the Cubs. If you want to be an ex-teammate of Sandberg's, and wind up in this steroid study, you have to wait. Either you have to be traded, or you have to wait until Sandberg retires. If you wait until Sandberg retires, you're going to be an OLD ex-teammate. And old players tend to get fewer at-bats than they did when they were younger.

On the other hand, Jose Canseco played for eight teams in his career. For the most part, if you wanted to be an ex-teammate of Canseco's, you just had to wait for him to move to another team. In the 1990s, that meant a maximum wait of two years, and an average wait of probably one year. That means it's very easy for you to wind up a young ex-teammate of Canseco's than a young ex-teammate of Sandberg's. And young players tend to get more at-bats as they get older and better.

Canseco's ex-teammates are younger than Sandburg's ex-teammates. That would explain whey they get more playing time, and that would also explain why they get better in subsequent seasons -- because they're still young enough to be improving, rather than declining. I can't prove it, but I bet that almost all the effect would disappear if the study properly controlled for age.

What this study actually demonstrates, I think, is that Jose Canseco switched teams a lot.

UPDATE: The authors have released a new version of the study, dated August 4. I haven't looked at it in depth, but one difference is that it now includes years up to 2009, instead of stopping at 2003.

One thing you'll notice in Table 7 is that 19 out of the 77 entries are significant at the 5% level. You'd have expected 4, not 19. Of course, they're not all independent, but still.

Also, Rafael Palmiero and Ken Griffey Jr. show as more extreme than Canseco, but in the other direction. That, I think, casts doubt on the hypothesis that there's something special about Canseco's numbers in this regard.

1 Comments:

What about park effects? They supposedly controlled for that in their study, but when they also control for team coaching by using a mangers record, I'm dubious of how much thought was put into this. That said, Canseco played in one of the worst hitting parks in the league for much of his career. Wouldn't we expect players who leave Oakland to hit more home runs based solely on that? Your example of Sandburg is the opposite, when you leave Wrigley, of course your home runs are more likely going to go down.